Over the last few episodes,
"Supernatural" has delivered some major shifts to the story's mythology, giving the Winchesters a new perspective on their family history and, for the first time, a home to call their own. In tonight's episode, "Trial and Error," there are more significant developments as Sam and Dean argue over who will complete a set of tests that will lead to information about closing the gates of hell.

Spoiler alert: Sam wins that particular battle. And in doing so, he may lose the war.

We sat down with
Jared Padalecki on set this week to discuss how the trials would impact Sam -- and suffice to say, it's not going to be pretty. "It's like a consumption," Padalecki says. "Like he's having Tuberculosis type [symptoms], hacking up blood and kind of trying to hide it from his brother. Nasty, but kind of cool."

For the first time, Sam and Dean seem to have a light at the end of the tunnel, at least when it comes to demons. "There is no finish line, but it is
a finish line," he says. "If they accomplish these trials, they can shut the gates of hell forever and keep demons out of earth, so they really want to do it. It's not easy, and it seems like something that could kill either one or both of the boys, but it's worth the trade-off in their opinion."

Things will definitely get ugly for Sam as the trials take a physical toll on him -- which is convenient, since Padalecki isn't exactly in fighting shape himself after taking a fall on the ski slopes over his holiday vacation. He's still nursing a broken rib.

"I'm concerned, as an actor, of what these trials are going to do to my character," Padalecki admits. "It's going to get pretty taxing ... He's starting to lose some of his physical prowess as well. Today we're doing a fight where Sam is really getting beat down because he's kind of lost a step ... so I'm concerned about how beat down Sam's going to get."

Check out our video interview below for much, much more from Jared -- including some discussion of Sam's love life, his dialogue with the show's writers, and yes...
that tweet he sent about his clothes falling off if he or Jensen Ackles won a People's Choice Award.